The present invention relates generally to a display apparatus. More particularly, the invention relates to a reflection type liquid crystal display apparatus for producing a color display having a high brightness, a high contrast and a high color purity without employing a back-light, by using external light, such as natural light, indoor light or the like.
As disclosed in Japanese Patent Application Laid-Open No. Heisei 9 (1997)-258219, Japanese Patent Application Laid-open No. Heisei 10 (1998)-161110, for example, the conventional reflection type liquid crystal display apparatus employing a single polarizing plate has a structure in which a pair of substrates formed with electrodes and orientation films, respectively, are arranged in opposition to each other and a liquid crystal layer is disposed between the substrates. One of the electrode is a reflecting electrode which serves as a reflection plate.
On the other hand, as disclosed in Japanese Patent Application Laid-Open No. Heisei 8 (1996)-166585, an electrode substrate on the side of the reflection plate is formed by providing a color filter and a flattening layer on a metal reflection plate, with a transparent electrode being formed thereover.
In the foregoing publications, both the reflection electrode and the reflection plate are formed with a thin metal film. Since the thin metal film has a low chemical strength and a low mechanical strength, it is easily oxidized or vulcanized, resulting in a lower reflectivity, and it is easily scratched. Accordingly, in the reflection electrode structure formed of an aluminum thin film, in which the electrode serves as a reflection plate, the surface of the aluminum thin film (reflection surface) inherently contacts the photosensitive resin, developer fluid, photosensitive resin peeling liquid, washing liquid (purified water) and the like during manufacture, to cause lowering of the reflectivity due to oxidization or corrosion of the surface in a process of patterning the aluminum thin film into the shape required for each electrode by way of a photolithographic process.
Furthermore, in the construction where the electrode serves as a reflection plate, the surface of the aluminum thin film which provides the reflection surface is exposed until the orientation film is formed. Therefore, the reflection surface inherently contacts the air to cause oxidization which will lower the reflectivity. Also, it is possible to scratch the reflection surface during the fabrication process, thereby lowering the process yield.
An aluminum terminal of the reflection electrode extended outside of a liquid crystal cell and exposed therefrom has a low mechanical strength and is easily oxidized or corroded, causing a difficulty in connecting with a tape carrier package (hereinafter referred to as TCP) mounting a liquid crystal driving IC or in peeling off the TCP for correction. Furthermore, it is also possible to cause an increase in the connection resistance or to cause a connection failure or display failure due to fluctuation.
In a construction where the transparent electrode is formed on the metallic reflection plate via the color filter and the flattening layer, since the color filter and the flattening layer are dielectric substances, viewed as an electric circuit, they form a capacitor structure. In this construction, since the reflection electrode is formed over the entire surface of the substrate, a structure is provided in which respective transparent electrodes are connected by capacitors. Therefore, the predetermined liquid crystal driving voltage applied to each transparent electrode may fluctuate due to capacitive coupling, thereby to cause degradation of the display quality.
On the other hand, since the color filter is directly formed on the metallic reflection plate, the surface of the metallic reflection plate (reflection surface) contacts the developer fluid, the washing liquid (pure water or the like) and so on to lower reflectivity due to oxidization or corrosion of the surface in the process for forming the color filter by way of photolithographic processing.
Furthermore, in case of a reflection type liquid crystal display apparatus employing a diffuse reflection electrode which is formed with an irregularity on the surface of the reflection electrode, since large number of irregularities will be present on the surface of the electrode within one pixel, the thickness of the liquid crystal layer (thickness of the liquid crystal layer between the substrates arranged in opposition) becomes non-uniform so as to cause a non-uniformity of the threshold voltage of the liquid crystal within the pixel, resulting in disturbance of the orientation of the liquid crystal molecule and a lowering of the contrast of the display.
In the reflection type liquid crystal display apparatus employing a diffuse reflection electrode, a gap between the substrates arranged in opposition across the liquid crystal layer is restricted by spacer beads. However, due to the irregularity on the reflection electrode, a difficulty is encountered in restricting the gap between the substrates with high precision, resulting in a non-uniformity of display or a lowering of the contrast.
In the reflection type liquid crystal display apparatus for color display employing a color filter, a multi-color display by tone control becomes possible. However, since an optical compensation by the liquid crystal and a phase difference film is not optimized, a monochrome display with good achromatic color cannot be obtained, and, thus, a color display with high color purity becomes difficult.
Furthermore, in the construction of the reflection electrode, where a display electrode serves as the reflection plate, when the color filter is provided on the substrate on the side of the reflection plate, the color filter is provided on the reflection electrode. Then, the voltage applied between the electrode arranged in opposition across the liquid crystal layer it, divided by the liquid crystal layer, the color filter and the orientation control layer so as to cause an elevating of the drive voltage.
The present invention has been developed in view of the problems set forth above. Therefore, it is an object of the present invention to provide a reflection type liquid crystal display apparatus which does not cause degradation of a reflection surface or an electrode terminal, provides a multiple color display with a high color purity, and reduces fluctuation of the voltage caused by loss of a drive voltage or capacitive coupling even when a color filter is provided on the substrate on the side of the reflection plate, thereby to realize a bright display having a high contrast.
According to one aspect of the present invention, a reflection type liquid crystal display apparatus comprises: a pair of substrates; a pair of orientation films disposed between the pair of substrates; a liquid crystal layer disposed between the pair of orientation films; a plurality of electrodes disposed respectively opposing the substrates and the orientation films; a reflection layer disposed between a plurality of the electrodes and the substrates within a space defined between one of the substrates and one of the orientation films; and at least one or more thin films having an insulating property arranged between the plurality of the electrodes and the reflection layer.
In the construction set forth above, a plurality of signal electrodes may be arranged on at least one substrate at an end portion thereof.
The reflection surface of the reflection layer may be a mirror surface.
The reflection layer may be a diffuse reflection surface having an irregularity on the surface thereof, the thin film having an insulating property serving as a flattening layer.
The reflection type liquid crystal display apparatus may further comprise a color filter disposed between the substrate and the orientation film.
The thin film having an insulating property may be formed with at least one of a reflection enhancing film consisting of two or more and no more than ten laminated dielectric films of an optical thickness of substantially one fourth wavelength, in which a dielectric film having a low refraction index and a dielectric film having a high refraction index are laminated alternately, a color filter, an insulation layer and a flattening layer.
The reflection type liquid crystal display apparatus may further comprise a black matrix arranged between pixels and peripheral portions of display regions within a space between the substrate and the orientation film arranged in opposition.
The reflection type liquid crystal display apparatus may further comprise a first birefringent film, a second birefringent film and a polarizing film arranged outside of the pair of substrates,
the liquid crystal layer may be formed of a nematic liquid having crystal a twist angle within a range of greater than or equal to 220xc2x0 and smaller than or equal to 270xc2x0,
a product of the anisotropy of the refraction index of the liquid crystal layer and a thickness of the liquid crystal layer is preferable in a range of greater than or equal to 0.74 xcexcm and less than or equal to 0.82 xcexcm, a product of the anisotropy xcex94n of the refraction index of the first birefringent film and the thickness thereof d is preferably in a range of greater than or equal to 160 nm and less than or equal to 220 nm, and a product of the anisotropy of the second birefringent film and the thickness thereof is preferably in a range of greater than or equal to 370 nm and less than or equal to 470 nm, and
with respect to a predetermined reference axis,
an angle of an absorption axis of the polarizing film is preferably greater than or equal to 120xc2x0 and less than or equal to 170xc2x0,
an angle of a lag axis of the first birefringent film is preferably less than or equal to 700 and less than or equal to 90xc2x0, and
an angle of a lag axis of the second birefringent film is preferably greater than or equal to 100xc2x0 and less than or equal to 140xc2x0.
The angle of the absorption axis of the polarizing film may be set at an angle of a transmission axis of the polarizing film.
The reflection type liquid crystal display apparatus may further comprise a light scattering layer disposed in at least one of an interlayer portion, in which the first and second birefringent films and the polarizing film are laminated.
The light scattering layer is formed by laminating from one to four light scattering layers.
The light scattering layer is formed by laminating light scattering layers having the same scattering characteristics or by laminating from two to four kinds of mutually distinct light scattering layers.
The reflection type liquid crystal display apparatus may further comprise a plurality of column like spacers for maintaining a gap for the liquid crystal layer.
According to the present invention, since the thin film having an insulating property is provided between the reflection layer and the transparent electrode, the an insulating thin film serves as a surface protection layer for the reflection layer to prevent the reflection surface from being scratched, oxidized or corroded so as to maintain high reflectivity. Also, since the electrode terminal connecting a TCP is formed with a transparent electrode which has a higher chemical strength than the metallic electrode, oxidation and corrosion of the surface of the electrode terminal can also be prevented to eliminate the possibility of occurrence of a connection failure due to an increase or fluctuation of the connection resistance of the TCP. Furthermore, the transparent electrode has a higher mechanical strength than the metallic electrode, so as to reduce the possibility of peeling of the layer or breakage upon peeling or re-connection of the TCP to facilitate correction, thereby to contribute to improvement of the production yield.
On the other hand, since the reflection layer is provided with a mirror surface as the reflection surface, the transparent electrode and the orientation film provided on the reflection layer via the insulating thin film may have a flat surface so as to make the thickness of the liquid crystal in the pixel uniform, thereby to avoid variation of the threshold voltage or fluctuation of the orientation so as to provides a high contrast display.
Also, the insulating thin film may prevent shorting or leakage between the reflection layer and the transparent electrode even when the reflection layer is formed of a conductive material, such as a metal, and serves to reduce variation of the liquid crystal driving voltage due to capacitive coupling formed between the reflection layer and the transparent electrode, thereby to prevent degradation of the display quality.
Even when the reflection layer is a diffuse reflection electrode having an irregularity on the surface, the insulating thin film serving as the flattening layer may successfully absorb or accommodate the irregularity on the surface of the reflection layer. Therefore, the surface of the transparent electrode and the orientation film formed over the reflection layer via the insulating thin film can be flat so as to make the thickness of the liquid crystal in the pixel uniform to avoid variation of the threshold voltage or fluctuation of the orientation, whereby a high contrast display is produced.
Furthermore, by providing the color filter, a multiple color display with high color purity can be realized.
Also, since the reflection enhancing film is provided on the reflection layer, a higher reflectivity is achieved than that obtained when the reflection layer is solely applied, thereby to produce a bright display.
Furthermore, even when the color filter is formed between the reflection layer and the transparent electrode, since the transparent electrode provided on the upper layer of the color filter contacts the liquid crystal layer across the orientation film, loss of voltage to be applied to the liquid crystal can be avoided even when the color filter is provided on the reflection layer side substrate. Therefore, the liquid crystal can be driven without causing an increase of the driving voltage.
Furthermore, by providing a black matrix between the pixels in the peripheral portion of the display region on the substrate, unnecessary reflection light from a non-display portion can be avoided, thereby to enable a color display with a high color purity and a high contrast.
Also, by optimizing the condition of the liquid crystal, the first birefringent film, the second birefringent film and the polarizing film, an achromatic black display and a white display can be obtained to produce a color display with a high color purity.
By providing the light scattering layer, a display with a natural view angle and without imprinting can be realized even when the reflection layer has a mirror surface.
Also, by combining the light scattering layers, a wide variety of view angle characteristics can be realized even with the same structure of liquid crystal display element.
Furthermore, by providing the column like spacers in the non-display portion, the gap between the substrates can be maintained at a high precision, thereby to realize a uniform display quality without fluctuation.
More particular features, advantages and effects of the present invention will become apparent from the following detailed description presented with reference preferred embodiment. It should be noted that the features, advantages and effects set forth above may be equally achieved by modification, application and combination of features discussed with reference to the particular embodiments.